1. Field of the Invention
The present invention relates to an imaging apparatus which converts an object image to an image signal via an imaging unit and has an image stabilizing function.
2. Description of the Related Art
Recently, an imaging apparatus as typified by a still camera and a video camera includes an image stabilizing device for correcting a vibration such as camera shake which is transmitted to the device from outside. Image stabilizing methods used in the image stabilizing device may include a method which is performed by moving an optical system (hereinafter referred to as an “optical image stabilizing method”) and a method which is performed by moving a charge-coupled device (CCD) as an image sensor (hereinafter referred to as a “CCD image stabilizing method”).
In the above described methods, a vibration correction amount for canceling a vibration is calculated by performing operations concentrating on a process for performing a predetermined frequency cutoff and an integral process in which units of an input and output are matched, with respect to a signal from a sensor for detecting the vibration (e.g., a gyro sensor). A vertical direction (pitch) and a horizontal direction (yaw) are typical directions in detecting the vibration, when the imaging apparatus is placed at a center of an orthogonal coordinate system (see FIG. 3).
The optical image stabilizing method removes the vibration from an image formed on an image sensor by moving a correction lens as a correction optical system by an amount for correcting the vibration using actuators driven on a plane in a direction perpendicular to each other. The CCD image stabilizing method removes the vibration from an image by moving an image sensor by an amount of the vibration by using actuators driven on a plane in a direction perpendicular to each other. Since both of the above methods relate to the method according to the present invention, constitution of the optical image stabilizing method will be described below as a representative example of the image stabilizing method.
In the imaging apparatus including the image stabilizing device, the correction lens to be controlled is moved to a target position by instructing the actuators to move the correction lens by an amount for correcting a vibration, and a present position of the correction lens is obtained at the time the correction lens is moved to the target position. Then, a feedback control is performed so as to make a deviation between the target position and the present position zero.
Japanese Patent No. 2,960,796 discusses a technique for determining an orientation of an imaging apparatus in which an obtained deviation of a correction lens or a change of an offset in the deviation caused by a gravitational force is detected as a change of a current value of an actuator. In the patent, a signal of a vibration sensor for detecting a vibration is also used while the orientation of the imaging apparatus is detected. Japanese Patent Application Laid-Open No. 2002-207232 discusses that a camera-shake correction property is switched according to a panning operation for shifting an imaging range in a horizontal direction and a tilting operation for shifting the imaging range in a vertical direction.
In general, in a system for detecting an orientation of an imaging apparatus by using a movable member such as a correction lens whose position changes by action of the gravitational force, a change of a present position of the movable member is regarded as a change of a deviation or a change of an offset contained in the deviation. Therefore, a change of the orientation can be determined based on the change of the present position. Similarly, when a predetermined acceleration is applied to the imaging apparatus while the imaging apparatus keeps the present orientation (when an external force other than the gravitational force, for example, the external force according to a panning operation is applied), the system behaves as if the gravitational force is acting on the movable member due to an inertial force.
In this case, an orientation of an image happens to be switched even when the orientation is not changed in the imaging apparatus, if, for example, the imaging apparatus has a function of switching the orientation of the image to be photographed or the orientation of the photographed image according to the orientation of the imaging apparatus. As a result, the image may be switched to an orientation a photographer does not intend, for example, when the photographer carries out a panning operation during taking images. Further, in a case where the photographed image is reproduced, the image happens to be switched to an orientation an observer does not expect.
As described above, in the system for detecting the orientation by using the movable member, it has been difficult to determine whether a force acting on the imaging apparatus is the gravitational force or an external force other than the gravitational force.